How Parasites Pull the Strings

Science fiction has long explored the terrifying possibility that we are devoid of free will, and that some unpleasant creature could control our minds. But mind control is not just a literary trope; it is also a common method by which parasites grow, reproduce, and complete their life cycles.

LIVERPOOL – Science fiction has long explored the terrifying possibility that we are devoid of free will, and that some unpleasant creature could control our minds or turn us into plodding zombies. But mind control is not just a literary trope. It is also a common method by which parasites gain access to environments where they can grow, reproduce, and complete their life cycles.

Consider the fungus Cordyceps, which interferes with the behavior of ants in tropical rainforests in such a way as to make them climb high into the vegetation, and latch onto a leaf to die. The fungus then reproduces by dropping its spores all over the forest floor, to infect more ants below. Similarly, a virus that infects gypsy moth larvae prompts them to climb en masse to the tops of trees to die. The virus then multiplies, and rains viral particles down on the forest floor.

These parasites make their hosts seek a higher elevation, which expands the reach of their infectious spores or particles. But other species can induce far more complex behaviors. Nematomorph worms, for example, infect crickets, and drive them to commit suicide by jumping into various water sources, be it a puddle or swimming pool. It is precisely in such aquatic environments that nematomorph worms reproduce and complete their life cycles.

In a documentary on the Senegal River and bilharzia, a local man said that anyone infected with bilharzia feels an imperious desire to go and pee in water, i.e. the river, and that is where the parasite's cycle continues. And in the same region, apparently the liver fluke infects small snails and drives them (agains their custom) to climb out of the water and up to the top of the grasses ( maybe typha) so that cows or other mammals eat them with the grass. Again, this completes the cycle. Fascinating stuff.

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